WEBVTT 0 00:06.110 --> 00:13.640 Now, unlike some other programming languages, if you've come from, say, C++, or Java, 1 00:13.910 --> 00:17.420 there is no such thing as Block Scope in Python. 2 00:17.450 --> 00:26.450 What this means is that if you were to create an if statement, say if 3 > 2: and 3 00:26.450 --> 00:32.960 if you were to create a new variable inside an if block, or a while loop, or a for loop, basically 4 00:32.960 --> 00:38.270 any sort of block of code that's indented, this does not count as a fence. 5 00:38.300 --> 00:43.220 It still has the same scope as its enclosing function, 6 00:43.220 --> 00:46.760 or if there's no enclosing function, then it has global scope. 7 00:46.790 --> 00:48.980 So let me show you a full example. 8 00:49.010 --> 00:54.830 Let's say we had a list of enemies so the enemies could be ["skeletons", "zombies", "aliens"]. 9 00:55.010 --> 01:01.700 So now if I was to define a game_level, right? Like the level that the user is currently playing at, 10 01:01.700 --> 01:08.630 let's say they're on Level 3 and I create an if statement and I check if the game_level is less 11 01:08.630 --> 01:10.310 than Level 5, 12 01:10.310 --> 01:16.110 well, in that case, I want to create a new_enemy, but I don't want the enemy to be too difficult to 13 01:16.140 --> 01:16.830 beat. 14 01:16.830 --> 01:22.020 So I'm going to pick from the list of enemies and I'm going to pick the first one. 15 01:22.410 --> 01:31.020 Notice how even though this new_enemy is a variable that's created within this if block if I go outside 16 01:31.020 --> 01:31.770 the if block, 17 01:31.770 --> 01:37.080 so I'm not indented at all anymore and I try to print this new_enemy, 18 01:37.680 --> 01:39.810 this is perfectly valid code. 19 01:39.810 --> 01:43.530 And if I run the code you'll see 'Skeleton' being printed. 20 01:43.740 --> 01:49.590 But notice how as soon as I embed this within a function. 21 01:49.890 --> 01:52.560 So let's define a new function. 22 01:53.250 --> 01:59.340 And now this line error is out because within the function there is local scope, 23 01:59.340 --> 02:03.900 so now this new_enemy is available anywhere within this function, 24 02:03.900 --> 02:11.400 because blocks like if, while, for, all of these blocks of code with colons and indentation, they don't 25 02:11.400 --> 02:13.590 count as creating a local scope. 26 02:13.590 --> 02:20.790 So in order to print this new_enemy, I actually have to be within the boundary of this function, which 27 02:20.790 --> 02:23.080 means my code has to be here. 28 02:23.890 --> 02:31.480 The most important thing to remember from this is if you create a variable within a function, then 29 02:31.480 --> 02:34.660 it's only available within that function. 30 02:34.780 --> 02:42.970 But if you create a variable within an if block, or a while loop, or a for loop or anything that has 31 02:42.970 --> 02:49.360 the indentation and the colon, then that does not count as creating a separate local scope. 32 02:49.450 --> 02:57.310 But one thing you might see when you're using some variable that is defined within a block, such as 33 02:57.310 --> 03:04.810 an if or a for is, you might get this warning from the linter, which reminds us how to write good 34 03:04.810 --> 03:10.690 Python code that the local variable might be referenced before assignment. 35 03:10.690 --> 03:16.960 So it's basically saying, well, what if the game_level is not less than five? 36 03:16.990 --> 03:19.810 What if it was like ten? 37 03:19.840 --> 03:26.620 Well, in this case, if we try to run this code, this print statement will never be executed because 38 03:26.620 --> 03:29.680 this if statement is not true. 39 03:29.680 --> 03:33.880 So this variable new_enemy is never created. 40 03:33.890 --> 03:36.170 So then what are we printing here? 41 03:36.170 --> 03:37.580 We're printing nothing. 42 03:37.580 --> 03:38.330 Just air. 43 03:38.360 --> 03:38.990 Right? 44 03:38.990 --> 03:46.100 So in order to get rid of this warning, what you can do is outside of any blocks, such as if, for, or 45 03:46.100 --> 03:51.710 while you can declare and create that variable and initialize it. 46 03:51.710 --> 03:55.790 So let's create new_enemy and set it to empty. 47 03:55.820 --> 04:02.030 Well, in this case, what it sees now is that there is a new_enemy variable. 48 04:02.030 --> 04:10.010 It has been already created, and depending on these conditions it might be modified, but it will always 49 04:10.040 --> 04:11.870 be able to be accessed. 50 04:11.870 --> 04:14.960 So the outcome doesn't really change. 51 04:14.960 --> 04:22.220 but the linter sees these situations where something could potentially go wrong and is just reminding 52 04:22.220 --> 04:22.610 you. 53 04:22.610 --> 04:23.990 So you have two choices. 54 04:23.990 --> 04:29.600 You can ignore it if you know what it's saying is complete rubbish because you know your code better 55 04:29.600 --> 04:38.450 than it does, or you can follow its orders and simply initialize the variable before you ever use it, 56 04:38.450 --> 04:45.170 and instead of creating the variable inside a block that may not be accessed.